envelope /enˈvəl-ōp/ noun

1. Something which envelops, wraps or covers
2. A cover for a letter (in this sense sometimes pronounced /onˈ/ or /ãˈ/ in imitation of French)
3. One of the coverings of a flower, the calyx or corolla (botany)
4. The gasbag of a balloon or airship
5. The locus of ultimate intersections of a series of curves (mathematics)
6. The outer containing vessel of a discharge tube (electronics)
7. The curve connecting the peaks of successive cycles of a modulated carrier wave (telecommunications)

envelˈoped adjective (heraldry)

Entwined, eg with serpents or laurels

envelˈopment noun

A complete wrapping or covering

envelope stuffer noun

1. A person who puts printed material into envelopes, eg for a charity
2. An item of promotional material enclosed with a letter, invoice, statement, etc (marketing)

envelope stuffing noun

on the back of an envelope (informal)

Said of a calculation that is performed quickly and without scrupulous regard to accuracy

push the envelope (informal)

To try to achieve more than seems possible